Lightweight High-Insulation Composite Structure Material for Cable Trench Roller Supports and Its Preparation Method

Abstract

This invention discloses a lightweight, high-insulation composite structural material for cable trench roller supports and its preparation method, belonging to the field of composite material engineering technology. It includes a three-dimensional woven continuous basalt fiber skeleton, a porous isolation layer embedded between the skeleton bundles, and an impregnated and cured insulating matrix. The porous isolation layer is pre-formed from chopped glass fibers and fumed silica via freeze-drying, and has internal capillary channels interconnected along the fiber bundle orientation. The insulating matrix is ​​a bisphenol A type epoxy cured product of dispersed nano-alumina and polyethersulfone. The oriented capillary channels act as distribution channels during the injection stage, changing the impregnation from pressure-driven to pore geometry-driven, thus reducing batch mechanical dispersion. After impregnation, the air is drained by capillary suction, leaving oriented closed air pores, which, together with the reduced basalt fiber volume fraction, serve as both dielectric and weight-reducing phases. The material density is no higher than 1.6 g / cm³. 3 Volume resistivity not less than 1×10 13 Ω·cm, and the three-point bending strength is not less than 220 MPa.

Description

Technical Field

[0001] This invention belongs to the field of composite material engineering technology, specifically relating to a lightweight, high-insulation composite structural material for cable trench roller supports and its preparation method. Background Technology

[0002] Cable trenches and tunnels are the main laying channels for transmission cables in urban power grids and large-scale industrial power distribution systems. Roller supports are used to support cables and reduce traction resistance during cable laying and long-term operation. For a long time, roller supports have primarily been made of steel, which presents three prominent problems. First, steel supports are too heavy. In large cable tunnels and deeply buried cable trenches, hundreds or even thousands of supports are often required for a single channel. This weight not only significantly reduces on-site installation efficiency but also continuously accumulates on the supporting structure of the cable tray, creating a cumulative load on the long-term load-bearing safety of the cable tray. Second, steel supports are conductive. In the case of dense parallel cable laying, alternating magnetic fields can induce alternating currents in the metal supports, forming circulating currents between adjacent supports, causing induced interference to cable operation and introducing additional losses. Third, steel supports are prone to corrosion in damp underground environments, resulting in high maintenance costs.

[0003] To overcome the aforementioned shortcomings of steel supports, fiber-reinforced polymer matrix composite supports, commonly known as fiberglass supports, have gradually gained application. These composite supports use continuous fibers as the reinforcing phase and thermosetting resin as the matrix, combining lightweight, insulation, and corrosion resistance. In principle, they can simultaneously address issues related to self-weight, induced current circulation, and corrosion. However, in engineering practice, existing composite supports have revealed common technical challenges, such as unstable bonding quality between the matrix and reinforcing fibers and high batch-to-batch dispersion of mechanical properties, hindering their widespread adoption in high-reliability power supply scenarios.

[0004] Korean patent KR101538032B1 discloses a basalt fiber reinforced composite material and its manufacturing method, which involves compounding basalt fibers with resin and then molding them using vacuum-assisted resin transfer molding. This method establishes the feasibility of basalt fiber as a cost-effective inorganic reinforcing phase; however, it employs a conventional layup impregnation method without specifically controlling the uniformity of impregnation in the dense regions between continuous fiber bundles, and it lacks a functional phase specifically for insulation reinforcement and a weight-reduction structure. Therefore, it struggles to solve the problems of batch-to-batch impregnation inconsistencies and high dispersion in mechanical properties.

[0005] US Patent Application US20080296046A1 discloses an electrical insulator and its manufacturing method, which uses a fiber-reinforced epoxy resin tube as a carrier and is covered with silicone rubber to provide hydrophobicity. This document explicitly states that insulators composed of two different materials have an interface between the tube body and the outer coating. Due to the difference in their thermal expansion coefficients, voids and delamination are easily generated at the interface, which can induce partial discharge and even surface flashover. This description reveals from the opposite perspective that interface voids and defects are key factors restricting insulation reliability. This solution relies on the outer silicone rubber coating for hydrophobic protection, resulting in a complex structure and making it difficult to fundamentally control interface defects.

[0006] US Patent 9093191B2 discloses a fiber-reinforced composite core for aluminum conductor cables, which consists of a continuous reinforcing fiber arranged unidirectionally in the longitudinal direction encapsulating a resin matrix, and a non-conductive insulating layer containing glass fiber is formed on the outer periphery. This approach verifies the technical route of obtaining mechanical properties through fiber orientation and insulation through a glass fiber layer in cable components. However, its unidirectional fiber arrangement and pultrusion impregnation method are only applicable to core materials with uniform cross-sections. It does not address the need for a three-dimensional braided structure with better load-bearing capacity, nor does it integrate the insulating phase, weight-reducing phase, and resin flow control phase in a multifunctional way, and it does not solve the inherent batch consistency problem in the vacuum injection molding process.

[0007] High batch-to-batch mechanical property dispersion has a particularly significant impact on engineering applications. Cable trench roller supports must withstand the dual loads of cable self-weight and laying traction over a long period. If the mechanical property dispersion of supports within the same batch is high, the design must use the lowest-performing individual in the batch as the safety margin benchmark, forcing the overall design to be conservative. This increases material usage and cost, and makes it difficult to guarantee the reliability of weaker individuals under long-term loads. The root cause of high dispersion lies in the uncertainty of resin wetting of the dense areas between continuous fiber bundles during vacuum infusion molding. This uncertainty causes random fluctuations in void content and interfacial bonding quality between batches. Therefore, making the resin wetting of the dense areas between continuous fiber bundles more deterministic and reproducible is key to reducing batch dispersion and improving the reliability of composite material supports in engineering.

[0008] Furthermore, in current vacuum-assisted resin transfer molding processes, a flow-guiding medium is typically laid to improve resin distribution in large-sized components, such as the flow-guiding mesh laid on the surface of the preform in a typical vacuum infusion process. However, this type of flow-guiding medium is an external sacrificial layer, which must be peeled off along with the release liner after curing. It does not participate in any function of the final component, and cannot serve as both a weight-reducing phase and an insulating phase. Moreover, it has limited improvement on the lateral wetting of the dense areas between continuous fiber bundles. In summary, the wetting of the dense areas between continuous fiber bundles in conventional vacuum infusion is dominated by injection pressure and channel randomness, resulting in large variance in void content between batches and unstable interfacial bonding quality, which in turn leads to high dispersion in mechanical properties. At the same time, the low-density phase introduced to achieve weight reduction usually comes at the cost of sacrificing wetting integrity, and the volume resistivity decreases due to moisture absorption at the new phase interface in humid environments. Therefore, simultaneously meeting the three objectives of lightweight, high insulation, and batch consistency for large cable tunnel roller supports has become an urgent technical problem to be solved. Summary of the Invention

[0009] To address the technical problem of simultaneously achieving lightweight, high insulation, and batch-to-batch mechanical property consistency in fiber-reinforced composite roller supports, the present invention aims to provide a lightweight, high-insulation composite structural material for cable trench roller supports and its preparation method. Through the synergistic combination of freeze-drying preforming and vacuum-assisted resin transfer molding, interconnected capillary channels oriented along the fiber bundles are constructed in situ between the fiber bundles of a three-dimensional woven continuous basalt fiber skeleton. During the infusion stage, these interconnected capillary channels act as resin distribution channels, transforming the impregnation of the dense region between the continuous fiber bundles from pressure-driven to channel geometry-driven. After impregnation, the channels are emptied via capillary suction, leaving behind oriented closed air pores that serve as both a dielectric insulating phase and a weight-reducing phase. This achieves significant weight reduction and high insulation while simultaneously reducing the batch-to-batch mechanical property dispersion.

[0010] To achieve the above objectives, the technical solution of the present invention is summarized as follows. The composite structural material of the present invention comprises a three-dimensional woven continuous basalt fiber skeleton, a porous insulating layer embedded in the region between adjacent fiber bundles of the skeleton, and an insulating resin matrix impregnated and cured in the skeleton and the porous insulating layer; wherein the porous insulating layer is pre-formed by freeze-drying a mixture of chopped glass fibers and fumed silica, and has capillary channels formed by ice crystal sublimation, oriented along the length of the fiber bundles and interconnected; the insulating resin matrix is ​​a bisphenol A type epoxy resin cured product dispersed with nano-alumina and polyethersulfone; the volume fraction of the continuous basalt fiber is 25%~35%, and the oriented interconnected capillary channels serve as resin distribution channels during the infusion stage and are emptied by capillary suction after impregnation, leaving oriented closed air pores. These oriented closed air pores constitute the dielectric insulating phase and weight-reducing phase of the material, synergistically with the reduced volume fraction of basalt fiber to ensure that the material density does not exceed 1.6 g / cm³.3 The present invention also provides a method for preparing the material, including steps such as slurry filling and directional freezing, freeze-drying to form pores and pre-consolidation, preparation of insulating resin, vacuum-assisted infusion and capillary drainage, and heating, curing and demolding.

[0011] Compared with the prior art, the present invention has the following beneficial effects. First, the capillary channels oriented and interconnected along the fiber bundle length direction serve as low-resistance priority channels to guide the rapid transport of resin during the vacuum infusion stage. At the same time, the mesopores between the pore walls provide lateral capillary wicking, changing the wetting of the dense region between continuous fiber bundles from dependence on injection pressure and random channels to dependence on pore geometry and surface energy. Since capillary-driven wetting is determined by reproducible pore geometry, the variance of void content is significantly reduced, and the batch-to-batch three-point bending strength dispersion is reduced from nearly 10% in existing FRP supports to about 3% to 4%. Second, after impregnation, because the capillary pores inside the continuous fiber bundle are much smaller than the macroscopic channels connecting the oriented capillary channels, the resin migrates from the macroscopic channels and fills the interior of the fiber bundle under the drive of capillary pressure difference. This essentially empties the macroscopic channels, leaving behind closed air pores oriented along the fiber bundle. These oriented closed air pores, with a low density close to that of air, constitute a weight-reducing phase. This, combined with the relatively low basalt fiber volume fraction (limited to 25%–35%), ensures that the material density does not exceed 1.6 g / cm³. 3 Compared to steel supports of the same specifications, it reduces weight by approximately 80%. Third, the oriented closed air pores enhance insulation with a low dielectric constant close to 1. Combined with the deep trapping mechanism of nano-alumina, the series high-resistivity barrier of the oriented silicon walls, and the hydrophobic end-capping of the fumed silica pore walls, these factors collectively suppress ionic conductivity in humid environments, ensuring that the material's volume resistivity is not less than 1×10⁻⁶. 13 The Ω·cm value meets the insulation safety requirements for high-voltage cable trench laying. Simultaneously, the lower basalt fiber volume fraction further enhances insulation by reducing the introduction of iron components from the basalt. The three-dimensional woven continuous basalt fiber skeleton ensures that the material's three-point bending strength is not less than 220 MPa. It should be noted that this value is a bending strength index at the material level, not the working stress of the support. Under the premise of reasonable design based on the actual load and cross-section of the support, ensuring that the rated working bending stress is lower than the material's allowable stress, it can meet the load-bearing requirements of the roller support for supporting the cable's self-weight and laying traction load. The specific load-bearing capacity and deflection of the support need to be calculated separately based on its cross-sectional geometry and the material's bending modulus. The aforementioned weight reduction, insulation, and consistency effects are synergistically achieved within the same material system, with each component exhibiting significant nonlinear synergistic gains. Most importantly, the resin distribution channel function of the oriented connected capillary channels during the injection stage and the weight reduction and dielectric functions remaining as oriented closed air pores after curing are decoupled in time and coexist, resolving the contradiction between the resin channels and the weight-reducing phase in conventional designs. Attached Figure Description

[0012] Figure 1 This is a comparison diagram of the three-point bending strength and its dispersion between the embodiments and comparative examples of the present invention. Detailed Implementation

[0013] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The following embodiments are used to illustrate the present invention and not to limit the scope of protection of the present invention. All equivalent modifications made based on the above content of the present invention fall within the scope of protection of the present invention. Unless otherwise specified, the raw materials used in the following embodiments are all commercially available industrial-grade products. The performance testing methods are detailed in the testing methods section below.

[0014] Example 1

[0015] This embodiment provides a lightweight, high-insulation composite structural material for cable trench roller supports, comprising a three-dimensional woven continuous basalt fiber skeleton, a porous insulating layer embedded in the region between adjacent fiber bundles of the skeleton, and an insulating resin matrix impregnated and cured therein; the porous insulating layer has bimodal capillary channels oriented along the length of the fiber bundles and interconnected. The specific manufacturing process of this embodiment is as follows.

[0016] First, a porous isolation layer slurry was prepared. Short-cut glass fibers with an average length of 6 mm and a specific surface area of ​​200 m² were used. 2 Fumed silica was mixed at a mass ratio of 3:2 with deionized water to prepare an aqueous slurry with a solid content of 12%. A silane coupling agent, γ-glycidoxypropyltrimethoxysilane, was added to the slurry at a dosage of 1.5% of the total mass of the chopped glass fibers and fumed silica. The slurry was dispersed under high-speed shearing for 30 min and then ultrasonically treated for 10 min to fully depolymerize the fumed silica and allow the silane to undergo preliminary hydrolysis and adsorption on the fiber and silica surfaces, resulting in a uniform and stable slurry. It should be noted that in this embodiment, hydrophobic long-chain alkyltrialkoxysilanes were not added to the aqueous slurry to avoid their hydrophobic segments causing hydrophobicity of the fumed silica in the aqueous phase, making uniform dispersion difficult. The hydrophobic end-capping of the long-chain alkyltrialkoxysilanes was performed on the dry pore walls in the gas phase after freeze-drying, as detailed below.

[0017] Subsequently, slurry filling and directional freezing were performed. The slurry was filled into the area between adjacent fiber bundles of a continuous basalt fiber skeleton pre-prepared using a three-dimensional weaving process, ensuring the slurry completely filled the inter-bundle voids. The filled skeleton was then placed in a directional freezing device, with one end in contact with a temperature-controlled cold end, establishing a temperature gradient along the fiber bundle length. The cold end was controlled to cool, causing ice crystals to grow directionally along the fiber bundle axis at a rate of approximately 25 μm / s, with a final temperature of -40°C. Under the action of the directional temperature gradient, the aqueous phase solidified directionally along the fiber bundle axis as columnar ice crystals, while fumed silica and chopped glass fibers were repelled and enriched in the interdendritic region, thus forming a continuous wall structure rich in fumed silica between the ice crystal skeletons.

[0018] The composite was then freeze-dried to form pores. After directional freezing, the composite was transferred to a freeze dryer, where ice crystals were sublimated for 48 hours at a cold trap temperature of -50°C and a vacuum level below 20 Pa. The spaces left by the in-situ sublimation of the ice crystals constituted capillary channels oriented along the fiber bundle axis and interconnected, resulting in a composite preform with an embedded oriented porous isolation layer. The porous isolation layer obtained in this embodiment exhibits a bimodal pore structure, where the equivalent pore size of the interconnected macroscopic channels oriented along the fiber bundle is approximately 150 μm, and the equivalent pore size of the mesoscopic pores located between the macroscopic channel walls is approximately 5 μm. The volume ratio of macroscopic channels to mesoscopic pores is approximately 1:0.5, the porosity of the porous isolation layer is 60%, the volume fraction of continuous basalt fibers in the composite material is 30%, and the volume of the porous isolation layer accounts for 25% of the composite material volume. After freeze-drying, the porous isolation layer was subjected to pre-consolidation and hydrophobic post-treatment in sequence: First, a 2% (w / w) polyvinyl butyral ethanol solution was sprayed onto the porous isolation layer as a temporary binder and volatilized and consolidated at 60°C, so that the porous isolation layer had sufficient self-supporting strength to withstand the subsequent vacuum infusion shear without collapsing; then, the dry preform was placed in a sealed container and treated with octyltriethoxysilane vapor at 60°C for 4 h to hydrophobically seal the residual silanol groups on the pore walls of the vapor-phase silica. The mass ratio of octyltriethoxysilane to the aforementioned γ-glycidoxypropyltrimethoxysilane was 1:6.

[0019] Then, the insulating resin was prepared. Bisphenol A type epoxy resin E51 was taken, and nano-alumina with an average particle size of 50 nm, pre-treated with γ-glycidoxypropyltrimethoxysilane, and a weight-average molecular weight of 3 × 10⁻⁶ were added. 4The polyethersulfone is prepared in a manner where the amount of nano-alumina added is 9% of the mass of the insulating resin matrix and the amount of polyethersulfone added is 12% of the mass of the insulating resin matrix. The polyethersulfone is dissolved in epoxy resin at 130°C and cooled. Then, the nano-alumina is uniformly dispersed by three-roll milling. Subsequently, methyl hexahydrophthalic anhydride curing agent with epoxy value stoichiometric ratio and 2,4,6-tris(dimethylaminomethyl)phenol accelerator accounting for 1% of the mass of epoxy resin are added. After stirring and degassing, the insulating resin is obtained. Optionally, to ensure that the material of the present invention meets the fire-retardant rating requirements of cable trenches and cable tunnels for the support structure, a halogen-free flame-retardant component can be further introduced into the above-mentioned insulating resin. For example, at least one of the halogen-free flame retardants such as phosphinates, aluminum hydroxide or magnesium hydroxide, and ammonium polyphosphate can be added. The amount added is sufficient to achieve the target flame-retardant rating without significantly impairing the mechanical and insulating properties. Since the flame-retardant component is dispersed in the insulating resin matrix, its introduction does not change the pore structure and capillary drainage pore-forming mechanism of the oriented porous isolation layer of the present invention. Therefore, flame-retardant function can be added while maintaining lightweight, high insulation and batch consistency.

[0020] Finally, vacuum-assisted resin transfer molding and curing are performed. The composite preform is placed in the mold cavity and vacuum-sealed. Vacuum is drawn and degassing is performed at a vacuum level of -0.095 MPa. Then, the resin inlet is opened, allowing the insulating resin to be rapidly distributed through the oriented capillary channels in the porous isolation layer under vacuum and to laterally impregnate the continuous fiber bundle. After impregnation, because the capillary pore size between the fibers inside the continuous fiber bundle is much smaller than the equivalent pore size of the macroscopic flow channel, it has a higher capillary suction pressure. Driven by the capillary pressure difference, the resin is drawn from the macroscopic flow channel and migrates into the interior of the continuous fiber bundle, causing the macroscopic flow channel to be basically emptied and leaving closed air pores along the fiber bundle orientation, until the interior of the continuous fiber bundle is completely wetted and the macroscopic flow channel is completely emptied. The vacuum is maintained and the temperature is increased to cure according to the program of curing at 80°C for 2 h, 120°C for 2 h, and 150°C for 2 h. After curing, the material is demolded to obtain the lightweight high-insulation composite structure material of the cable trench roller bracket of this embodiment.

[0021] The density of the material obtained in this embodiment was measured to be 1.52 g / cm³. 3 The volume resistivity is 4.2 × 10⁻⁶. 13The density is Ω·cm, the three-point bending strength is 258 MPa, the three-point bending modulus is 21 GPa, the coefficient of variation of the three-point bending strength of ten samples in the same batch is 3.2%, the defect-type void content is 0.6%, the volume fraction of oriented closed air pores formed by macroscopic channel drainage is 18%, and the volume resistivity retention rate after absorbing moisture for 168 h in an environment of 40°C and 95% relative humidity is 92%. All indicators meet the design requirements of lightweight, high insulation and batch consistency. The above density is calculated by the mixing law and confirmed by the water displacement method based on the continuous basalt fiber volume fraction of 30% and the oriented closed air pore volume fraction of 18%, and the two are in good agreement. Furthermore, the material in this embodiment exhibits a water absorption rate of 0.4% after immersion in deionized water at 23°C for 24 hours, and retains 90% of its three-point bending strength after 168 hours of moisture absorption treatment. The low water absorption rate and high wet strength retention indicate that the oriented, interconnected capillary channels, after impregnation, are separated into independent, closed air pores that do not communicate with the outside world due to capillary blockage within the continuous fiber bundles, thus failing to form a continuous water absorption pathway. This is consistent with the fact that the defective void content in this embodiment is only 0.6%. The measured three-point bending modulus provides a material stiffness basis for subsequent calculation of the bearing arm deflection based on the cross-sectional geometry of the support.

[0022] Further microstructural and multi-scale performance characterization of the material in this embodiment was performed. Scanning electron microscopy observation showed that the macroscopic channels within the porous isolation layer were arranged parallel to the fiber bundle axis, interconnected, and well-permeable. The walls of the macroscopic channels were composed of continuous walls enriched with fumed silica and chopped glass fibers, with mesoscopic pores of approximately 5 μm equivalent pore size distributed between the walls. After curing, the macroscopic channels were basically emptied, forming closed air pores oriented along the fiber bundle, with dense and intact pore walls. The mesoscopic pores and the interior of the continuous fiber bundles were densely filled with resin and tightly bonded to the pore walls, with no obvious debonding or defect-type interface voids observed. The fibers and resin were fully impregnated inside the continuous basalt fiber bundles, and no visible dry spots were observed on the cross-section. Dynamic thermomechanical analysis showed that the glass transition temperature of the material in this embodiment was 158°C, which was about 12°C higher than the control without polyethersulfone, indicating that the introduction of polyethersulfone improved the heat resistance of the matrix to adapt to the temperature cycling conditions of the cable trench. The thermal conductivity of the material in this embodiment, measured by laser scintillation, is 0.46 W / (m·K), approximately 1.5 times higher than that of the pure epoxy matrix. This is beneficial for the dissipation of heat generated during cable operation and also helps to homogenize the heat distribution during curing and reduce batch-to-batch variance of residual stress. The interlaminar shear strength test result is 42 MPa, further confirming that the chemical bonding interface established by silane coupling between the inorganic phase and the organic matrix has good load transfer capability.

[0023] Example 2

[0024] This embodiment provides a lightweight, high-insulation composite structural material for cable trench roller supports. Its structure and preparation process are basically the same as those in Embodiment 1. The difference lies in the use of a higher continuous basalt fiber volume fraction, a larger equivalent pore size of the macroscopic flow channel, and a higher porosity of the porous isolation layer, in order to examine the feasibility of material performance under high fiber loading and large pore size conditions.

[0025] In preparing the porous isolation layer slurry, the mass ratio of chopped glass fibers to fumed silica was 3:2, and the amount of γ-glycidoxypropyltrimethoxysilane was 3% of the total mass of the chopped glass fibers and fumed silica. The mass ratio of octyltriethoxysilane to γ-glycidoxypropyltrimethoxysilane used in the hydrophobic post-treatment after freeze-drying was 1:3. After the slurry was filled between the three-dimensionally woven continuous basalt fiber skeleton bundles, it underwent directional freezing. Since this embodiment aims to obtain macroscopic channels with larger pore sizes, a low ice crystal growth rate of 5 μm / s along the fiber bundle axis was adopted to allow for sufficient ice crystal growth. The final temperature was -40°C, followed by freeze-drying to form pores and pre-consolidation. The resulting porous isolation layer has a bimodal pore structure. The equivalent pore size of the connected macroscopic flow channels along the fiber bundle orientation is 300 μm, and the equivalent pore size of the inter-wall mesoscopic pores is 10 μm. The volume ratio of macroscopic flow channels to mesoscopic pores is 1:1. The porosity of the porous isolation layer is 75%. The volume fraction of continuous basalt fibers in the composite material is 35%, and the volume of the porous isolation layer accounts for 35% of the volume of the composite material.

[0026] When preparing the insulating resin, the amount of nano-alumina added is 15% of the mass of the insulating resin matrix, with an average particle size of 100 nm, and pretreated with γ-glycidoxypropyltrimethoxysilane; the amount of polyethersulfone added is 20% of the mass of the insulating resin matrix, with a weight-average molecular weight of 5 × 10⁻⁶. 4 The curing agent was methyltetrahydrophthalic anhydride, and the accelerator was 2,4,6-tris(dimethylaminomethyl)phenol. The material of this embodiment was obtained by vacuum-assisted resin transfer molding, followed by temperature curing and demolding according to the same procedure as in Example 1.

[0027] The density of the material obtained in this embodiment was measured to be 1.53 g / cm³. 3 The volume resistivity is 3.5 × 10⁻⁶. 13 The material exhibits a strength of 270 MPa at three points and a three-point flexural modulus of 24 GPa. The coefficient of variation for the three-point flexural strength of ten samples from the same batch is 3.9%. The defect-type void content is 0.9%, the volume fraction of oriented closed air pores formed by macroscopic channel depletion is 22%, and the volume resistivity retention rate after 168 h of moisture absorption is 90%. Under the conditions of 35% basalt fiber volume fraction and 75% porosity, the high fiber loading and high volume fraction of oriented closed air pores work synergistically to ensure that the material density does not exceed 1.6 g / cm³. 3The insulation and mechanical properties, as well as batch consistency, all meet the design requirements, indicating that the present invention can still stably achieve the expected results at higher fiber loading and larger pore sizes.

[0028] Microstructural observation of the material in this embodiment shows that, under conditions of 75% porosity and 300 μm equivalent pore size of macroscopic channels, the porous isolation layer still maintains good orientation connectivity and pore wall structure integrity. The resin is rapidly distributed through the macroscopic channels with larger pore size and then laterally impregnates the continuous fiber bundle through the mesoscopic pores. After impregnation, the macroscopic channels are emptied by capillary suction, leaving behind large-scale oriented closed air pores. After curing, no through-hole defects caused by high porosity are observed, indicating that the oriented porous structure of the present invention still has robust impregnation control and pore-forming ability at high fiber loading and large pore size.

[0029] Example 3

[0030] This embodiment provides a lightweight, high-insulation composite structural material for cable trench roller supports. Its structure and preparation process are basically the same as those in Embodiment 1. The difference lies in the use of a lower continuous basalt fiber volume fraction, a smaller equivalent pore size of the macroscopic flow channel, and a lower porosity of the porous isolation layer, in order to examine the feasibility of material performance under low fiber loading and small pore size conditions.

[0031] In preparing the porous isolation layer slurry, the mass ratio of chopped glass fibers to fumed silica was 3:2, and the amount of γ-glycidoxypropyltrimethoxysilane was 0.5% of the total mass of chopped glass fibers and fumed silica. The mass ratio of octyltriethoxysilane to γ-glycidoxypropyltrimethoxysilane used in the hydrophobic post-treatment after freeze-drying was 1:10. After the slurry was filled between the three-dimensionally woven continuous basalt fiber skeleton bundles, it underwent directional freezing. Since this embodiment aims to obtain a fine porous structure with a small pore size, a relatively high ice crystal growth rate of 50 μm / s along the fiber bundle axis was adopted to suppress excessive ice crystal growth. The final temperature was -40°C, followed by freeze-drying to form pores and pre-consolidation. The resulting porous isolation layer has a bimodal pore structure. The equivalent pore size of the connected macroscopic flow channels along the fiber bundle orientation is 50 μm, the equivalent pore size of the inter-wall mesoscopic pores is 0.5 μm, the volume ratio of macroscopic flow channels to mesoscopic pores is 1:0.2, the porosity of the porous isolation layer is 40%, the volume fraction of continuous basalt fibers in the composite material is 25%, and the volume of the porous isolation layer accounts for 15% of the volume of the composite material.

[0032] When preparing the insulating resin, the amount of nano-alumina added is 3% of the mass of the insulating resin matrix, with an average particle size of 20 nm, and pretreated with γ-glycidyl etheroxypropyltrimethoxysilane; the amount of polyethersulfone added is 5% of the mass of the insulating resin matrix, with a weight-average molecular weight of 1×10⁻⁶. 4The curing agent was methylhexahydrophthalic anhydride, and the accelerator was 2,4,6-tris(dimethylaminomethyl)phenol. The material of this embodiment was obtained by vacuum-assisted resin transfer molding, followed by temperature curing and demolding according to the same procedure as in Example 1.

[0033] The density of the material obtained in this embodiment was measured to be 1.54 g / cm³. 3 The volume resistivity is 5.4 × 10⁻⁶. 13 The three-point bending strength was 235 MPa, the three-point bending modulus was 18 GPa, the coefficient of variation of the three-point bending strength of ten samples in the same batch was 3.5%, the defect-type void content was 0.7%, the volume fraction of oriented closed air pores formed by macroscopic channel venting was 12%, and the volume resistivity retention rate after 168 h of moisture absorption was 93%. Under the lower limit conditions, with a low fiber volume fraction and a small amount of nano-alumina, the material still meets all design requirements for density, insulation, mechanics, and consistency. In particular, the lower basalt fiber volume fraction reduces the introduction of iron components. The volume resistivity of this embodiment is the highest among the three embodiments, which, conversely, confirms the beneficial effect of moderately reducing the basalt fiber volume fraction on improving insulation. As can be seen from Examples 1 and 2, the ranges defined in this invention, including 3%~15% nano-alumina content, 5%~20% polyethersulfone content, 50~300 μm equivalent pore size of macroscopic channels, 0.5~10 μm equivalent pore size of mesoscopic pores, 40%~75% porosity, 25%~35% basalt fiber volume fraction, 12%~22% volume fraction of oriented closed air pores, and 15%~35% volume ratio of porous isolation layer, are all supported by the data from the examples at the lower limit, median, and upper limit. Among them, the axial growth rate of ice crystals corresponds inversely to the equivalent pore size of macroscopic channels, that is, a lower growth rate of 5 μm / s corresponds to a larger pore size of 300 μm, a higher growth rate of 50 μm / s corresponds to a smaller pore size of 50 μm, and a median of 25 μm / s corresponds to a medium pore size of 150 μm, which is consistent with the physical law that the lower the freezing rate in directional solidification, the more fully the ice crystals grow.

[0034] Example 4

[0035] This embodiment provides a cable trench roller bracket component made using the material of the present invention, illustrating the feasibility of the material in actual bracket molding. The composition and process parameters of this embodiment are the same as in Embodiment 1, the difference being that a three-dimensional braided continuous basalt fiber skeleton is pre-woven into the outline shape of the roller bracket, and a molding die matching the bracket's shape is used accordingly. Specifically, a three-dimensional braiding path is designed according to the structure of the support arm and roller mounting base of the bracket body, and the braiding density is appropriately increased in areas where the support arm experiences greater stress. After filling the fiber bundle regions of the braided skeleton with chopped glass fiber and fumed silica slurry, a temperature gradient is applied along the length of the support arm for directional freezing, causing oriented capillary channels to be arranged along the main stress direction of the support arm, followed by freeze-drying to form pores. Insulating resin is prepared, and the composite preform is placed in the bracket molding die for vacuum-assisted resin transfer molding. After curing according to the programmed temperature rise, the component is demolded to obtain an integrally molded roller bracket component.

[0036] The density of the obtained stent component was measured to be 1.53 g / cm³. 3 The volume resistivity is 4.0 × 10⁻⁶. 13 The three-point bending strength of the bearing arm is 255 MPa (Ω·cm), with a coefficient of variation of 3.4%. The content of defective voids is 0.7%, and the volume fraction of oriented closed air pores is 18%, which is basically consistent with the flat plate sample of Example 1. This indicates that the material and its preparation process of the present invention can adapt to the actual molding requirements of the roller bracket and can maintain the comprehensive performance of lightweight, high insulation and batch consistency in irregular bearing structures. Field simulation laying tests showed that the weight of a single installed bracket was reduced by about 80% compared with steel brackets of the same specification, significantly improving installation efficiency. Furthermore, no induced circulating current was detected between brackets under parallel laying conditions.

[0037] Comparative Example 1

[0038] The only difference between this comparative example and Example 1 is that, instead of directional freezing along the fiber bundle length, the porous isolation layer is prepared by directly freezing the skeleton of the filling slurry in a -40°C cold storage followed by freeze-drying. This results in a randomly oriented, non-interconnected porous structure in the isolation layer. All other components and processes are the same as in Example 1. This comparative example is used to verify the necessity of this distinguishing technical feature of interconnected capillary channels along the fiber bundle orientation. The density of the material in this comparative example is measured to be 1.53 g / cm³. 3 The volume resistivity is 2.6 × 10⁻⁶. 13The three-point flexural strength was 205 MPa, the coefficient of variation was 9.6%, the content of defective voids was 3.4%, and the volume resistivity retention rate after moisture absorption was 90%. It can be seen that after eliminating the oriented interconnected channels, the channels are random and unconnected, which makes it impossible to form directional voids through capillary suction after impregnation. The lateral wetting of the resin also loses geometric guidance. The content and dispersion of defective voids increase significantly, and the three-point flexural strength decreases significantly compared with Example 1.

[0039] Comparative Example 2

[0040] The only difference between this comparative example and Example 1 is that the porous isolation layer is not included; instead, the three-dimensional braided continuous basalt fiber skeleton is directly injection molded with the same insulating resin via vacuum-assisted resin transfer molding. All other conditions remain the same. This comparative example is used to verify the function of the porous isolation layer as both a weight-reducing phase and a resin distribution channel. The density of the material in this comparative example was measured to be 1.78 g / cm³. 3 The volume resistivity is 1.9 × 10⁻⁶. 13 The material exhibits a strength of 228 MPa at three points (Ω·cm), a coefficient of variation of 8.0%, a defect-type void content of 2.7%, and a volume resistivity retention rate of 88% after moisture absorption. This demonstrates that after removing the porous isolation layer, the inter-beam region is completely filled with resin without oriented closed air pores, increasing the material density to 1.78 g / cm³. 3 The concentration should not exceed 1.6 g / cm³. 3 The weight reduction requirement is not met, and the dense area between continuous fiber bundles is not sufficiently wetted due to the lack of a dedicated distribution channel, resulting in high dispersion.

[0041] Comparative Example 3

[0042] The only difference between this comparative example and Example 1 is that no silane coupling agent was added during the preparation of the porous isolation layer slurry, and no hydrophobic post-treatment was performed after freeze-drying. The chopped glass fibers and the surface of the fumed silica were not chemically modified; all other conditions were the same. This comparative example serves as a control that retains the oriented porous structure while removing the interfacial molecular design, used to verify the independent contribution of the silane coupling system. The density of the material in this comparative example was measured to be 1.52 g / cm³. 3 The volume resistivity is 8.2 × 10⁻⁶. 12 The three-point bending strength was 195 MPa, the coefficient of variation was 3.6%, the defect-type void content was 0.8%, and the volume resistivity retention rate after moisture absorption was 71%. It is evident that, under the premise of retaining the oriented channels and thus maintaining a low defect-type void content and dispersion, removing the silane coupling leads to a lack of covalent bonding between the fumed silica pore walls and the epoxy matrix, forming a weak interface. This results in a significant decrease in the three-point bending strength, and the residual silanol groups absorb moisture, causing the volume resistivity to drop to 8.2 × 10⁻⁶. 12 The Ω·cm and the moisture retention rate after absorption are only 71%, both of which do not meet the design requirements.

[0043] Comparative Example 4

[0044] The difference between this comparative example and Example 1 is that it does not apply directional freezing to achieve a random porous structure in the isolation layer, nor does it add a silane coupling agent or undergo hydrophobic post-treatment; all other conditions are the same. This comparative example involves a dual baseline removal process that simultaneously eliminates both the underlying orientation architecture and the interface molecular design, serving as a benchmark for calibrating their synergy. The density of the material in this comparative example was measured to be 1.55 g / cm³. 3 The volume resistivity is 1.5 × 10⁻⁶. 13 The baseline sample exhibits the worst mechanical strength, batch dispersion, and insulation retention after moisture absorption. Its three-point bending strength is 182 MPa, coefficient of variation is 11.2%, defect-type void content is 3.6%, and volume resistivity retention after moisture absorption is 73%.

[0045] Comparative Example 5

[0046] The only difference between this comparative example and Example 1 is that the amount of nano-alumina added is 20% of the mass of the insulating resin matrix, exceeding the upper limit of 3%~15% specified in this invention; all other conditions are the same. This comparative example is used to verify the technical significance of the nano-alumina content range. The density of the material in this comparative example was measured to be 1.55 g / cm³. 3 The volume resistivity is 9.0 × 10⁻⁶. 12 The resistance values ​​are: Ω·cm, three-point bending strength: 245 MPa, coefficient of variation: 5.4%, defect-type void content: 1.1%, and volume resistivity retention rate after moisture absorption: 88%. This indicates that excessive nano-alumina agglomerates, and these agglomerates become charge transport channels and stress concentration sources, causing the volume resistivity to decrease instead of increase to 9.0 × 10⁻⁶. 12 The decrease in Ω·cm and mechanical strength confirms the necessity of limiting the content of nano-alumina to 3%~15%.

[0047] Comparative Example 6

[0048] The only difference between this comparative example and Example 1 is that polyethersulfone is not added when preparing the insulating resin; all other conditions are the same. This comparative example serves as a component-deficient control to verify the contribution of polyethersulfone to the batch-to-batch mechanical property dispersion. The density of the material in this comparative example was measured to be 1.50 g / cm³. 3 The volume resistivity is 4.0 × 10⁻⁶. 13The three-point bending strength was 218 MPa with a coefficient of variation of 8.7% (Ω·cm), the defect-type void content was 0.9%, and the volume resistivity retention rate after moisture absorption was 91%. It is evident that after removing polyethersulfone, the epoxy matrix exhibits brittle fracture with dispersed fracture behavior, causing the coefficient of variation of the three-point bending strength to increase to 8.7% and the strength to decrease significantly compared to Example 1. This indicates that the phase separation toughening effect of polyethersulfone plays an irreplaceable role in homogenizing fracture behavior and reducing the dispersion of convergent mechanical properties.

[0049] Detection methods

[0050] The performance of the embodiments and comparative examples of this invention was determined as follows. Density was determined using the Archimedes displacement method, calculated based on the principle of buoyancy from the mass of the sample in air and deionized water. Each sample was measured three times, and the average value was taken. Volume resistivity was determined using the three-electrode method. A 1000 V DC voltage was applied to both ends of the sample using a high-resistivity meter, connecting the protective electrode, the protected electrode, and the measuring electrode. To eliminate interference from polarization current and environmental factors, the resistivity reading was taken after 20 minutes of pressure application to calculate the volume resistivity. Three-point bending strength was determined according to the corresponding fiber-reinforced plastic bending performance test standard on a universal testing machine under conditions of a span-to-sample thickness ratio of 16:1 and a loading rate of 2 mm / min. Ten parallel samples were measured in each group.

[0051] The batch mechanical property dispersion was characterized by the coefficient of variation of the three-point bending strength of ten parallel samples from the same batch. The coefficient of variation is the ratio of the standard deviation of strength to the average strength; the smaller the value, the better the batch consistency. The void content was determined using microscopic image analysis. After grinding and polishing the sample cross-section, images were created under a metallographic microscope, and the proportion of void area within the cross-section was statistically analyzed and converted into a volume fraction. The method for determining the volume resistivity retention rate after moisture absorption was as follows: the sample was placed in a constant temperature and humidity chamber at 40°C and 95% relative humidity for 168 hours, then removed and dried. The volume resistivity was re-measured using the three-electrode method described above. The ratio of the volume resistivity after moisture absorption to that before moisture absorption was used as the retention rate to characterize the long-term stability of the material's insulation performance in a humid cable trench environment. The porosity of the porous insulating layer was calculated from the apparent volume of the insulating layer and the actual volume of the constituent solid phase. The equivalent pore diameter and volume ratio of macroscopic channels and mesoscopic pores were determined by mercury intrusion porosimetry combined with scanning electron microscopy image analysis.

[0052] The main instruments and parameters used in the testing of this invention are as follows: Density testing was performed using an electronic density balance with a weighing accuracy of 0.0001 g. Volume resistivity testing was performed using a high-resistivity meter with a three-electrode system, with a test voltage of 1000 V, an ambient temperature of 23°C, and a relative humidity of 50%. Three-point bending strength and interlaminar shear strength were determined using an electronic universal testing machine with a load sensor range of 10 kN. Void content and pore morphology were determined using a scanning electron microscope combined with a metallographic microscope and a mercury porosimeter, with the mercury porosimeter pressure range covering the equivalent pore diameter from 0.5 μm to 300 μm. Glass transition temperature was determined using a dynamic thermomechanical analyzer at a frequency of 1 Hz and a heating rate of 3°C / min, with the peak loss factor temperature as the glass transition temperature. Thermal conductivity was determined using the laser scintillation method. Moisture absorption treatment was performed using a constant temperature and humidity test chamber with a temperature control accuracy of 0.5°C and a humidity control accuracy of 2%. The volume fraction of oriented closed air pores was calculated by combining the apparent density of the composite material with the actual densities of the continuous basalt fibers, cured resin, and pore wall solid phases according to the mixing law. Scanning electron microscopy (SEM) image analysis confirmed their axial orientation along the fiber bundles and their independent, closed morphology. This invention strictly distinguishes between oriented closed air pores and defective voids. Oriented closed air pores are engineered pores that are actively constructed, oriented, and regularly shaped by capillary drainage after directional freezing and impregnation. Defective voids refer to randomly generated, randomly oriented pores due to poor wetting. The former includes the weight-reducing phase and dielectric phase, while the latter includes the void content. The two are distinguished by their morphological and orientational characteristics in the microscopic images. The three-point flexural modulus and three-point flexural strength were determined in the same bending test and calculated using the flexural modulus formula based on the slope of the initial linear segment of the load-deflection curve combined with the specimen span and cross-sectional dimensions. The method for determining the mass water absorption rate is as follows: The sample is immersed in deionized water at 23°C for 24 hours, then removed, dried, and weighed. The ratio of the mass increase before and after immersion to the mass before immersion is used as the mass water absorption rate, which characterizes the sealing of the oriented closed air pores and its moisture resistance. The method for determining the retention rate of the three-point bending strength after moisture absorption is as follows: The sample is subjected to moisture absorption at 40°C and 95% relative humidity for 168 hours, then removed and the three-point bending strength is re-measured according to the bending test method described above. The ratio of the three-point bending strength after moisture absorption to the three-point bending strength before moisture absorption is used as the retention rate, which characterizes the long-term stability of the material's mechanical properties in a humid cable trench environment. For each of the above tests, at least three parallel samples are taken in each group, and the results are taken as the arithmetic mean. The coefficient of variation for bending strength dispersion is calculated using the test values ​​of ten parallel samples from the same batch.

[0053] The key performance test results of the above embodiments and comparative examples are summarized in Table 1 to compare and analyze the contribution of each technical feature and their synergistic relationship.

[0054] Table 1 Summary of key performance data for the examples and comparative examples

[0055]

[0056] As shown in Table 1, although the composition and process parameters of Examples 1 to 3 were taken from the median, higher fiber loading, and lower fiber loading, respectively, within the specified range, the density of all three examples consistently remained at approximately 1.5 g / cm³. 3 And not higher than 1.6 g / cm 3 At the same time, it must satisfy the requirement that the volume resistivity is not less than 1×10 13 The three-point bending strength is not less than 220 MPa and the coefficient of variation is at a low dispersion level of about 3% to 4%, while each comparative example fails to meet the standard in at least one of the indicators. This allows for a quantitative demonstration of the nonlinear synergistic effect of each technical feature. Taking the three-point bending strength as an example, the double-baseline removal comparative example 4 only achieves 182 MPa when there is neither orientation structure nor interface coupling; the comparative example 3, which retains the orientation structure but removes the interface coupling, achieves 195 MPa, an increase of 13 MPa relative to the baseline, because the weak interface becomes the strength bottleneck; the comparative example 1, which removes the orientation structure but retains the interface coupling, achieves 205 MPa, an increase of 23 MPa relative to the baseline, because the random hole structure introduces defect-type voids that limit the strength; while the comparative example 4, which removes the orientation structure but retains the interface coupling, achieves 205 MPa, an increase of 23 MPa relative to the baseline, because the random hole structure introduces defect-type voids that limit the strength; and the comparative example 3, which retains the orientation structure but removes the interface coupling, achieves 205 MPa, an increase of 23 MPa relative to the baseline, because the random hole structure introduces defect-type voids that limit the strength. Figure 1 As shown in the comparison, Example 1, which simultaneously possesses the orientation architecture and interface coupling, achieves 258 MPa, a 76 MPa improvement over the baseline, far exceeding the sum of the contributions of the two individual features (36 MPa), exhibiting a significant nonlinear synergy where one plus one is far greater than two. The mechanism lies in the fact that the orientation architecture eliminates defective voids, and the interface coupling strengthens the bonding strength; both must be present simultaneously to overcome the two independent strength bottlenecks of voids and weak interfaces. Regarding batch dispersion, Comparative Examples 1 and 4, which removed the orientation architecture, have coefficients of variation as high as 9.6% and 11.2%, respectively, while Comparative Example 3, which retained the orientation architecture, still has a coefficient of variation as low as 3.6% even after removing the coupling, indicating that connecting capillary channels along the fiber bundle orientation is the dominant feature for converging batch dispersion. Regarding insulation retention after moisture absorption, Comparative Example 3, which removed the hydrophobic silane end caps, has a retention rate of only 71%, while Example 1 reaches 92%, confirming the crucial role of silane coupling and hydrophobic end caps in long-term insulation stability under humid conditions.

[0057] It also exhibits synergistic characteristics in terms of volume resistivity. Comparative Example 3, with the removal of interfacial coupling and hydrophobic end caps, shows a volume resistivity reduced to 8.2 × 10⁻⁶. 12 The volume resistivity of the high-surface-area fumed silica was below the design requirements, and the retention rate after moisture absorption was only 71%, indicating that the pore walls of the high-surface-area fumed silica would become an insulation bottleneck in humid environments if not hydrophobically sealed. Meanwhile, the volume resistivity of Comparative Example 5, which had an excessive amount of nano-alumina, also decreased to 9.0 × 10⁻⁶. 12The Ω·cm indicates that the insulation performance does not increase monotonically with the filler content. Only when the oriented silicon wall series barrier, the nano-alumina deep trap, and the hydrophobic end cap work synergistically and are each within a defined range can a stable insulation performance of not less than 1×10⁻⁶ be achieved in Examples 1 to 3. 13 The volume resistivity of Ω·cm and the moisture retention rate of over 90% further confirm the nonlinear synergistic relationship between the various technical features of this invention.

[0058] The synergistic gains of this invention stem from the causal recursion and closed-loop feedback between the innovation in the underlying orientation architecture and the innovation in molecular design. The interconnected macroscopic channels along the fiber bundle orientation within the porous isolation layer serve as low-resistance priority channels to guide the rapid longitudinal transport of resin, while the mesoscopic pores between the macroscopic channel walls provide lateral capillary wicking pressure, actively pulling the resin into the dense region within the continuous fiber bundle. This transforms the wetting process, which was originally dominated by injection pressure and random channels, into a wetting process dominated by reproducible pore geometry and surface energy, causing the variance of void content to converge. This is the fundamental reason for the reduction in batch mechanical property dispersion. Furthermore, since the capillary pores between fibers inside the continuous fiber bundle are much smaller than the macroscopic channels, after impregnation, the resin migrates from the macroscopic channels and fills the interior of the fiber bundle under the drive of capillary pressure difference, causing the macroscopic channels to be basically emptied and leaving closed air pores along the fiber bundle orientation. These oriented closed air pores strengthen insulation with a low dielectric constant close to one on the one hand, and form a weight-reducing phase with a low density close to air on the other hand. This decouples the resin distribution channel function of the oriented connected capillary channels during the pouring stage from the weight reduction and dielectric functions after curing in time, thus resolving the contradiction that the resin channels must be filled with resin while the weight-reducing phase must retain gaps, which is mutually exclusive in conventional designs. This is the key to the present invention's ability to ensure complete wetting, low voids, and high insulation while significantly reducing density. While addressing the wetting issue, the orientation architecture also introduces new interface problems. The high specific surface area of ​​the fumed silica pore walls is rich in silanol groups, which, without chemical bonding, form a weakly hygroscopic interface. Therefore, γ-glycidoxypropyltrimethoxysilane is introduced to covalently bridge the silica walls with the epoxy matrix, and its epoxy end participates in the anhydride curing network. The residual silanol groups remaining after coupling are prone to capillary condensation and ionic conductivity in the humid cable trench environment. Therefore, after freeze-drying, the residual silanol groups are further sealed in the fumed state with long-chain alkyltrialkoxysilane. This sequential design of interface bonding and hydrophobic sealing simultaneously achieves the triple functions of interface bonding, pore wall hydrophobization, and long-term insulation stability. In addition, the hydrophobic pore walls, in turn, enhance the function of the orientation-closed air pores as a dielectric isolation phase, forming a closed-loop feedback.

[0059] At the resin matrix level, nano-alumina and polyethersulfone each play multiple synergistic roles. Nano-alumina, on the one hand, increases volume resistivity by trapping migrated charges through deep traps; on the other hand, its thermal conductivity, which is much higher than that of epoxy, homogenizes curing exothermics and reduces batch variance of residual stress, thereby addressing and reinforcing the core objective of batch mechanical property consistency. Polyethersulfone, through the co-continuous phase formed by phase separation, not only toughens and arrests cracks but also homogenizes the fracture behavior of the matrix, further converging the dispersion of three-point bending strength and increasing the glass transition temperature of the matrix to adapt to the temperature cycling of the cable trench. Thus, the underlying orientation architecture is the cause, and the molecular design of the interface and matrix is ​​the effect. The innovation of each molecular design respectively addresses and reinforces the three core objectives of weight reduction, insulation, and consistency, forming a triple closed causal chain. The absence of any link will lead to the cascading collapse of the synergistic effect, which is the fundamental reason why the performance of each comparative example in Table 1 deteriorates significantly after removing a single feature.

[0060] In summary, the various technical features of this invention constitute a closed causal chain, starting from the underlying orientation architecture, progressively extending towards the interface and matrix molecular design, and ultimately reinforcing the three core objectives. The bimodal capillary channels connected along the fiber bundle orientation are the cause, which, while eliminating voids and reducing dispersion, introduces the interface challenge of high specific surface area silicon walls; silane coupling and hydrophobic end-capping, as effects, precisely respond and reinforce the dielectric isolation function. Dense wetting introduces the problem of uneven curing heat release; the high thermal conductivity of nano-alumina, as an effect, reinforces batch consistency. The brittle matrix introduces the problem of dispersed fracture behavior; the phase separation toughening of polyethersulfone, as an effect, reinforces mechanical consistency. These three causal branches are respectively closed around the three core objectives of weight reduction, insulation, and consistency, intertwined and inseparable. The absence of any link will trigger a cascading collapse of the synergistic effect. This is the essence that distinguishes this invention from the simple superposition of known components in existing technologies, and it is also the fundamental guarantee for its significant progress in lightweighting, high insulation, and batch consistency simultaneously.

[0061] The chemical mechanism of the interface and curing system of this invention can be explained from four levels: silane coupling, epoxy curing, charge transport inhibition, and directional solidification phase separation. At the silane coupling level, the γ-glycidoxypropyltrimethoxysilane molecule has a hydrolyzable trimethoxysilyl group at one end and a glycidyl ether epoxy group at the other. During the slurry dispersion stage, the trimethoxysilyl group first undergoes hydrolysis to generate a silanol group. This reaction can be represented as the methoxy group of the silane reacting with water to remove methanol and generate the corresponding silanol. The generated silanol group then condenses with the silanol groups on the surfaces of fumed silica, basalt fibers, and chopped glass fibers to form stable siloxane-silicon covalent bonds, thereby anchoring the silane to the inorganic phase surface. This condensation reaction can be represented as the dehydration condensation of silanols on the inorganic phase surface with silane and silanol to generate siloxane-silicon bonds and release water molecules. Fumed silica has a high specific surface area of ​​up to 200 m². 2The high silanol areal density provides abundant reaction sites for the aforementioned anchoring.

[0062] At the epoxy curing level, the glycidyl ether epoxy end of the silane anchored on the inorganic phase surface participates in the curing reaction using anhydride as the curing agent, together with the epoxy group of bisphenol A type epoxy resin E51. The tertiary amine accelerator 2,4,6-tris(dimethylaminomethyl)phenol first causes the anhydride to open its ring, generating a carboxylate group. The carboxylate group then attacks the epoxy group, causing it to open its ring and generating an ester bond and a new alkoxy anion. The newly formed alkoxy anion then attacks another anhydride molecule, and this process continues alternately until a three-dimensional cross-linked network is formed. Because the epoxy end of the silane is covalently woven into this network, the inorganic phase surface forms a continuous covalent transition layer with the organic matrix through silane bridges, thereby upgrading the interface from physical adhesion to chemical bonding. This is the chemical essence of the significant decrease in the three-point bending strength after the removal of silane in Comparative Example 3.

[0063] At the level of charge transport suppression, the increase in volume resistivity of the material is achieved through the superposition of three mechanisms. First, the deep trap effect: the interface formed between nano-alumina and the epoxy matrix introduces deep-level traps, which can capture charge carriers migrating under an electric field, thereby reducing the effective carrier mobility. Second, the barrier cascading effect: the oriented fumed silica pore walls formed by directional solidification enrichment constitute a series of high-resistivity barriers in the direction perpendicular to the leakage current, forcing the leakage path to become more circuitous and prolonged. Third, the hygroscopic suppression effect: the hydrophobic pore walls capped with long-chain alkylsilanes prevent capillary condensation of water molecules on the high specific surface area silica walls, thereby cutting off the ionic conductivity channels provided by the adsorbed water film in humid environments. It is worth noting that when the nano-alumina content exceeds the upper limit, the particle spacing becomes too small and agglomeration occurs. These agglomerates not only lose the charge-trapping effect of isolated deep traps but may also form local charge transport channels at particle overlaps, becoming stress concentration sources. This is precisely the mechanism behind the decrease in volume resistivity in Comparative Example 5.

[0064] At the directional solidification phase separation level, the directional freezing process follows the anisotropic solidification law of solutions or suspensions under directional temperature gradients. When a temperature gradient is established along the fiber bundle length, ice crystals preferentially nucleate at the cold end and grow directionally into columnar crystals along the temperature gradient direction. At the ice crystal growth front, fumed silica particles and chopped glass fibers are repelled by the growing ice crystal front due to size effects and enriched in the residual liquid phase between dendrites. After the ice crystals sublimate, interconnected channels oriented along the fiber bundle axis remain at the original ice crystal location, while the enriched solid phase constitutes the continuous walls between the channels. The freezing rate is a key process parameter for controlling the channel size. A lower freezing rate is conducive to the full growth of ice crystals to form macroscopic channels with larger pore sizes, while a higher freezing rate forms a finer pore structure. This invention limits the ice crystal growth rate along the fiber bundle axis to 5~50 μm / s precisely to obtain mesoscopic pores within this range that possess both low-resistance longitudinal transport macroscopic channels and lateral wicking capabilities, thereby forming a bimodal pore structure that is conducive to uniform wetting. It should be noted that the oriented closed air pores described in this invention are engineered pores actively constructed through capillary drainage after directional freezing and impregnation. Their orientation, connectivity, and volume fraction are all controllable and adjustable by process parameters such as freezing rate, porosity, and pore size ratio. This is fundamentally different from the defect-type voids randomly generated due to poor wetting during vacuum infusion. The former, as the weight-reducing phase and dielectric phase, is the source of the beneficial effects of lightweighting and high insulation in this invention, while the latter is the root cause of mechanical property dispersion and strength degradation. The two are completely different in their causes, morphology, orientation, and function. This distinction is key to correctly understanding how this invention maintains low defects and high consistency while significantly reducing weight. The chemical and physical mechanisms at the above four levels are coupled with each other, jointly supporting the synergistic achievement of lightweighting, high insulation, and batch consistency in this invention.

[0065] In terms of load-bearing and interfacial load transfer, the three-dimensional woven continuous basalt fiber skeleton is the primary bearer of the material's mechanical properties. Basalt fiber, obtained by melting and drawing natural volcanic rock, possesses high tensile strength and a surface rich in silanol groups and metal oxide active sites. After silane coupling treatment, it can form a strong chemical bond interface with epoxy matrix, ensuring that the load borne by the fiber can be effectively transferred to the matrix and evenly distributed between the fibers. The three-dimensional woven structure interweaves the fiber bundles in three directions, significantly improving interlayer bonding and anti-delamination ability compared to unidirectional lay-ups or two-dimensional fabrics. This avoids the defect of unidirectional composite materials being prone to splitting along the fiber direction, which is the structural basis for the present invention's three-point bending strength of not less than 220 MPa and the ability to maintain corresponding strength even with irregularly shaped load-bearing arms. A porous insulating layer embedded between the fiber bundles acts as a weight-reducing phase, lowering density without weakening the main load-bearing path of the continuous fiber skeleton. Instead, it ensures sufficient wetting of the fiber bundles through oriented capillary channels, making the load transfer between the fiber and the matrix more complete. This is the key to the present invention's ability to maintain high mechanical properties while significantly reducing weight. It should be specifically pointed out that the aforementioned three-point bending strength is a material-level destructive strength index, characterizing the material's ultimate ability to resist bending failure, and is a different physical quantity from the working stress of the support under rated load. Whether the support meets the load-bearing requirements should be evaluated under the premise of reasonable design according to its actual load and cross-section, ensuring that the rated working bending stress is lower than the material's allowable stress (i.e., the material's bending strength divided by the corresponding safety factor). The high bending strength provided by the three-dimensional braided continuous basalt fiber skeleton of this invention provides sufficient strength margin for this evaluation. At the same time, the load-bearing capacity of the cable support is also controlled by deflection, which is mainly determined by the material's bending modulus and the geometry of the support cross-section rather than by bending strength. The material of this invention has a measured three-point bending modulus of not less than 18 GPa, which is higher than the typical level of similar unsaturated polyester molding compounds, providing a stiffness basis for controlling the deflection of the load-bearing arm. In addition, polymer-based composite materials exhibit creep effects under continuous loads. Therefore, for long-term load conditions, in addition to instantaneous bending strength, the creep rupture strength of the material should also be calculated based on the service life to ensure reliability under long-term loads.

[0066] From a capillary dynamics perspective, the improvement in wetting uniformity due to the bimodal pore structure of the porous isolation layer can be further explained. In vacuum-assisted resin transfer molding, the flow of resin in a porous medium is dominated by the competition between viscous forces and capillary forces. The ratio between the two can be characterized by the capillary number; the smaller the capillary number, the more dominant the capillary force and the more stable the flow front. The interconnected macroscopic channels along the fiber bundle orientation have lower flow resistance due to their larger equivalent pore size, allowing the resin to be transported longitudinally rapidly at lower injection pressures, thereby reducing the dominance of viscous forces during flow. At the same time, the mesoscopic pores with equivalent pore sizes only in the micrometer range between the macroscopic channel walls generate significant lateral capillary pressure, actively pulling the resin from the macroscopic channel into the dense region of adjacent continuous fiber bundles. Since the capillary pressure is determined by reproducible physical properties such as pore size and surface tension, rather than by batch-to-batch fluctuations in injection pressure and random channels, the bimodal pore structure makes the driving force for lateral wetting more stable and reproducible. This is the essence of capillary dynamics: the convergence of void content variance and the reduction of batch mechanical dispersion. When the volume ratio of macroscopic channels to mesoscopic pores deviates from the specified range, either due to the excessive proportion of macroscopic channels resulting in insufficient lateral core suction, or due to the excessive proportion of mesoscopic pores resulting in obstructed longitudinal transport, it is not conducive to uniform wetting. Therefore, the present invention limits the volume ratio of the two to 1:0.2~1:1.

[0067] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A lightweight, high-insulation composite structural material for cable trench roller supports, characterized in that: The composite structural material comprises a three-dimensional woven continuous basalt fiber skeleton, a porous insulating layer embedded in the region between adjacent fiber bundles of the skeleton, and an insulating resin matrix impregnated and cured in the skeleton and the porous insulating layer; the porous insulating layer is pre-formed by freeze-drying a mixture of chopped glass fibers and fumed silica, and the porous insulating layer has capillary channels formed by ice crystal sublimation, oriented along the length of the fiber bundles and interconnected; the insulating resin matrix is ​​a cured product of bisphenol A type epoxy resin, in which nano-alumina and polyethersulfone are dispersed, and the content of nano-alumina is [missing information]. The insulating resin matrix comprises 3% to 15% by mass, and the polyethersulfone content comprises 5% to 20% by mass of the insulating resin matrix. The oriented interconnected capillary channels serve as resin distribution channels during the vacuum-assisted resin transfer molding stage, guiding the resin to impregnate the fiber bundle. After impregnation, capillary suction causes the resin to migrate from the oriented interconnected capillary channels and fill the interior of the fiber bundle, resulting in at least partial emptying of the oriented interconnected capillary channels and the formation of closed air pores along the fiber bundle orientation. These closed air pores constitute the dielectric isolation phase and weight-reducing phase of the composite material. The density of the composite material is not higher than 1.6 g / cm³. 3 Volume resistivity not less than 1×10 13 Ω·cm.

2. The lightweight, high-insulation composite structural material for cable trench roller supports according to claim 1, characterized in that, The capillary channel has a bimodal pore structure, including a connected macroscopic channel with an equivalent pore size of 50~300 μm along the fiber bundle orientation, and a mesoscopic pore with an equivalent pore size of 0.5~10 μm located between the walls of the macroscopic channel. The volume ratio of the macroscopic channel to the mesoscopic pore is 1:0.2~1:

1.

3. The lightweight, high-insulation composite structural material for cable trench roller supports according to claim 1, characterized in that, The chopped glass fibers and fumed silica are treated with γ-glycidyl etheroxypropyltrimethoxysilane before freeze-drying, and the amount of γ-glycidyl etheroxypropyltrimethoxysilane is 0.5% to 3% of the total mass of the chopped glass fibers and fumed silica.

4. The lightweight, high-insulation composite structural material for cable trench roller supports according to claim 3, characterized in that, After freeze-drying and before vacuum-assisted resin transfer molding, the porous isolation layer is further subjected to hydrophobic post-treatment with alkyltrialkoxysilane having 8 to 16 carbon atoms by vapor deposition or solvent impregnation. The mass ratio of the alkyltrialkoxysilane to the γ-glycidoxypropyltrimethoxysilane is 1:3 to 1:

10.

5. The lightweight, high-insulation composite structural material for cable trench roller supports according to claim 1, characterized in that, The porosity of the porous isolation layer is 40%~75%, the volume fraction of continuous basalt fiber in the composite structural material is 25%~35%, the volume fraction of the oriented closed air pores is 12%~22%, and the volume of the porous isolation layer accounts for 15%~35% of the volume of the composite structural material.

6. The lightweight, high-insulation composite structural material for cable trench roller supports according to claim 1, characterized in that, The nano-alumina has an average particle size of 20~100 nm and is pretreated with γ-glycidoxypropyltrimethoxysilane.

7. The lightweight, high-insulation composite structural material for cable trench roller supports according to claim 1, characterized in that, The polyethersulfone has a weight-average molecular weight of 1×10⁻⁶. 4 ~5×10 4 The curing agent of the cured product is an acid anhydride curing agent, selected from at least one of methylhexahydrophthalic anhydride and methyltetrahydrophthalic anhydride, and the accelerator is 2,4,6-tris(dimethylaminomethyl)phenol.

8. The method for preparing the lightweight, high-insulation composite structural material for cable trench roller supports as described in any one of claims 1 to 7, characterized in that, Includes the following steps: Step 1: Short-cut glass fibers and fumed silica are dispersed in water to obtain a slurry. The slurry is filled into the region between adjacent fiber bundles of a three-dimensional woven continuous basalt fiber skeleton. A temperature gradient is applied along the length of the fiber bundles for directional freezing to crystallize water into oriented ice crystals. The ice crystals are then freeze-dried to sublimate, forming a porous isolation layer with interconnected capillary channels along the fiber bundle orientation in situ within the region. The porous isolation layer is then pre-consolidated to give it self-supporting strength to withstand infusion shear, resulting in a composite preform. Step 2: Bisphenol A type epoxy... Nano-alumina and polyethersulfone are added to the resin and dispersed evenly. Then, an anhydride curing agent and an accelerator are added to obtain an insulating resin. In step three, the composite preform is placed in a mold, and the insulating resin is distributed through the oriented connected capillary channels and laterally impregnated into the fiber bundle by vacuum-assisted resin transfer molding. After impregnation, the resin is transferred from the oriented connected capillary channels to fill the fiber bundle by capillary suction, so that the oriented connected capillary channels are at least partially emptied to form oriented closed air pores. In step four, the composite structure material is obtained by demolding after heating and curing.

9. The preparation method according to claim 8, characterized in that, In step one, the growth rate of ice crystals along the fiber bundle axis during directional freezing is 5~50 μm / s. The chopped glass fibers and fumed silica are treated with γ-glycidyl etheroxypropyltrimethoxysilane before or during dispersion in water. After freeze-drying, the porous isolation layer is hydrophobically treated by vapor deposition or solvent impregnation with alkyltrialkoxysilanes having 8~16 carbon atoms.

10. The preparation method according to claim 8, characterized in that, In step three, the vacuum degree of the vacuum-assisted resin transfer molding is below -0.095 MPa. In step four, the curing is carried out sequentially at 80°C for 2 hours, 120°C for 2 hours, and 150°C for 2 hours.

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